Uncertainty-based rejection (confidence thresholding) provides negligible improvement against behaviorally overlapping unknown services. In I2P, XGBoost rejection recovery is +0.0% Macro-F1; FreeNet known-service mean confidence is 97.75% vs. unknown-service 97.95%, making threshold-based separation impossible. Only Tor exhibits partial confidence separation (known 81.22% vs. unknown 67.66%), enabling XGB recovery of +8.5%.
From 2026-saleem-open-world-darknet-traffic — Open-World Darknet Traffic Recognition Under Leave-One-Service-Out Evaluation
· §IV-D, Table IV
· 2026
· arXiv preprint
Implications
Circumvention protocols whose flows behaviorally resemble trained service categories will evade confidence-based anomaly rejection; designing flows to sit in the behavioral overlap zone of known services is a viable evasion strategy against this class of classifier.
Tor's partial confidence separation (mean 67.66% vs. 81.22% for known services) suggests that onion-routing traffic inherently produces enough behavioral distinctiveness to partially trigger uncertainty-based rejection — a property other protocols could intentionally exploit by injecting timing or size variability.